Conventional washing machines typically include a cabinet which receives a stationary tub for containing wash and rinse water. A wash basket may be rotatably mounted within the wash tub. A drive assembly and a brake assembly can be positioned with respect to the wash tub and configured to rotate and control the rotation of the wash basket within the wash tub to cleanse the wash load placed into the wash basket. During e.g., a wash or spin cycle, water is typically extracted from the wash load by rotating the wash basket containing the wash load at high rotational speeds. Centrifugal forces pull the majority of the water out of the wash load and through perforations in the rotating basket. A pump assembly can be used to rinse and drain the extracted water to a draining system.
The rotating basket is typically supported by a suspension system designed to dampen translational motion induced by any imbalance within the rotating basket. High stresses are sometimes encountered within the basket, drive system, and suspension system during the high-speed spin action used for water extraction during normal wash cycles and may create unbalance within the washer. With an unbalance within the wash load, a force is generated which is proportional to the product of the mass of the load, the distance between the imbalance and the center of rotation of the tub, and the square of the velocity of the tub. Small imbalances can very easily generate large forces as a result of the high rotational velocities that may cause unbalance. When a load is out of balance, excess vibration and noise may cause damage to the washing machine.
Known washing machines may employ various sensing techniques to determine if the machine is operating with an unbalanced load. One technique may include current or load sensing in the motor control. When an unbalanced load is detected during an extraction spin cycle, the machine is stopped and a signal is generated to alert the user to the unbalanced load. Sensing techniques involving current or load sensing in the motor control can be inaccurate due to additional loads on the motor other than the load provided by any imbalance.
Another unbalance detection technique previously used may include a power filter preprogrammed in the washing machine controller. The variables of the machine may be considered and programmed prior to the appliance leaving the manufacturing factory. No further changes are made to the power filter and an out of balance detection may be inaccurate.
Thus, a need exists for an improved system and method for sensing unbalance in a washing machine that dynamically monitors the load size and calculates a power filter to limit power or torque based on the load size. A system and method for detecting unbalance that provides for improved unbalance detection dynamically as water is extracted from the tub may be particularly useful.